Conventional wisdom says you can pretty much eat whatever you want if you’re an avid runner, as your body is burning off all of the excess calories. But is that really true? New research now suggests that avid runners need to pay attention to their diets as well when it comes to the potential for heart disease.

As a 10-mile-a-day runner, Dave McGillivray thought he could eat whatever he wanted without worrying about his heart. “I figured if the furnace was hot enough, it would burn everything,” said McGillivray, who is 59.

But a diagnosis six months ago of coronary artery disease shocked McGillivray, a finisher of 130 marathons and several Ironman-distance triathlons. Suddenly he regretted including a chocolate-chip-cookie recipe in his memoir about endurance athletics.

“My first reaction was, I was embarrassed,” he said.

As race director of the Boston Marathon, McGillivray is a high-profile exhibit in a growing medical case against the devil-may-care diets of many marathoners. Their high-mileage habit tends to lower their weight, blood pressure, heart rate and cholesterol levels, leading them (and sometimes their doctors) to assume their cardiac health is robust regardless of diet.

“‘I will run it off’—that attitude clearly prevails among the marathoners themselves, almost sometimes to an arrogance,” said Paul Thompson, a veteran marathoner who is chief of cardiology at Hartford Hospital.

A growing body of research shows the error of that thinking. A study published in the current edition of Missouri Medicine found that 50 men who had run at least one marathon a year for 25 years had higher levels of coronary-artery plaque than a control group of sedentary men. A British Medical Journal study published this year compared the carotid arteries of 42 Boston Marathon qualifiers with their much-less active spouses. “We hypothesized that the runners would have a more favourable atherosclerotic risk profile,” says the article. As it turned out, that hypothesis was wrong.

Many assumed that extreme-endurance sports could help prevent heart disease, but now the research suggests this extreme activity may actually cause problems.

We should be careful of course to jump to conclusions after several studies, but certainly this raises questions and challenges old assumptions.

It also brings us back to some common sense notions that moderation in diet and excercise can be the best combination. Pushing anything to the limit – whether its your diet or your activities, can lead to risks.

Jamey Codding is scheduled to run his first marathon in Chicago on October 9th. Jamey was a competitive runner in the past, but mainly ran 5K’s or under. He began running again after a long break and has had to educate himself on in-race hydration and nutrition. If you’re interested in running at all, and want to start off on the right foot, you’ll definitely want to read the first part of his series, Training for Marathon #1: Hydration and Nutrition.

1. Running will give you a heart attack or other heart problems. It is true that exercise temporarily raises the odds of a heart attack while you’re mid-workout, but doing it consistently reduces that risk over the long haul, leading to a net benefit. Some researchers have questioned whether marathon running, especially in people who haven’t trained a lot, might cause heart damage, at least temporarily. But there’s no evidence that it causes long-term harm or actually leads to heart attacks. Even athletes with enlarged hearts—if they’re healthy hearts—aren’t, as once feared, at risk of early death. The bottom line: Simply going for a run most days of the week is doing far more good than bad for your heart.

2. Running will ruin your bones and joints. A study in the August issue of the American Journal of Preventive Medicine found no evidence of accelerated rates of osteoarthritis among long-distance runners when compared with healthy nonrunners. “We used to say that osteoarthritis came from wear and tear. That’s now revised to say that is can result from tear but not wear,” says James Fries, emeritus professor of medicine at the Stanford University School of Medicine and senior author of the study. Moreover, weight-bearing exercise like running helps stave off osteoporosis by maintaining bone mineral density.

3. Running will kill you before your time. According to a study published this week in the Archives of Internal Medicine, running and other vigorous exercise in middle age is associated with a longer life. Not only that, it will make your later years more pleasant by reducing disability. After tracking runners and healthy nonrunners for 21 years, starting when they were at least 50 years old, a research team led by Stanford’s Fries found that the ability to perform activities of daily life like getting out of a chair and walking was better among runners than nonrunners. And 19 years into the study, 15 percent of the runners had died, compared with 34 percent of the nonrunners.USNews.com

People who engage in very repetitive tasks such as long distance running, labor or swimming show very little or no improvement in the size and strength of their muscles. Long distance events are by nature very low in intensity.

Compare a marathon runner to a 100 meter sprinter. Marathon runners who train for very long periods at a very low intensity are emaciated looking having less than normal muscle mass and carry on average 14 ? 16% body fat. Sprinters, on the other hand, who train for short periods at a high level of intensity are very muscular and have half the body fat levels than marathoners. If cardio is the key to getting lean, as many people presume, why do marathoners have a higher body fat than sprinters? The reason is, a specific stimulus is required for a specific outcome.

The specific stimulus needed to stimulate muscle and strength is high intensity training. This is a universal training principle that affects everyone without exception. This is due to the fact that we are anatomically and physiologically the same. If this were not true doctors could not perform surgery and prescribe medicine. Consequently, the stimulus needed to induce biochemical changes that build muscle and strength in humans is the same.

Intensity, when referring to training, is the percentage of physical exertion that one is capable of. Training with one hundred percent intensity is the best way, the only way, to stimulate muscular size and strength in the shortest amount of time. How does one gauge the intensity of their workouts? By taking your working sets to positive or concentric failure.

Taking a set to the point of failure, where you cannot possibly perform another rep despite your maximum effort is one of, and perhaps the most important of several factors in your success. There are many who disagree and advocate high volume training with 60%, 72%, 95%, or whatever percentage of intensity they decide is the best. Some even claim training all out, with one hundred percent intensity is not only unnecessary, but detrimental. Over the years I’ve seen so called strength coach specialists, and personal trainers with 15 letters after their last names, concoct the most ridiculous routines, using almost every percentage, that have yet to show any effectiveness in real world application.

The main problem with these bogus routines is that there are only two accurate measures of intensity. Zero, when you are at rest; and 100%, when you?re training to the point of failure. How do you measure anything less than 100% intensity? If I can do 10 repetitions to complete failure with 100 pounds on the leg extension machine, where do I go for 80% intensity? Do I perform 10 reps with 80 pounds? Or do I use 100 pounds and only perform 8 reps? Is 80% the optimum percentage, or is it 65%? There is no evidence that suggests, let alone proves, anything less than 100% effort is equally or more effective. Are you starting to see the ridiculousness and inaccuracy of such training prescriptions?

Intensity cannot be measured accurately with reps or weight. While performing a set, intensity increases exponentially with each successive rep. Performing the first 5 reps on the leg extension is not equivalent in intensity to performing the last 5 reps. Hence, 5 reps is not the equivalent of 50% intensity.

The only way to train that is completely accurate is with all out intensity to failure. This will give you a concrete view of how you?re performing. If you train with 100% intensity during every workout and you do not progress, you know you are not recovering. There will never be a question whether you are providing a strong enough stimulus for progress. However, if you follow the percentage of intensity or the percentage of max rep principles, how will you know you are training intensely enough to stimulate muscular size and strength? If you plateau, are you training too hard or too long? Do you lower the percentage or raise it? Do you need more rest, or do you need to train at a higher intensity? There is no need for this guessing game.

Your goal is to bring about the largest, most rapid outcome for your individual genetic potential. In order for this to occur, the body requires 100% intensity every working set of every exercise. This is the only truly accurate way to gauge the efficacy of your training program. Nothing less than 100% will do. The body needs a reason to adapt. Give it!